Living organisms activate transcriptions of suitable genes to various stimuli received from their environments thereof. Accordingly, suitable proteins are synthesized to adapt to various environments. The above transcriptions of genes are controlled by nucleotide sequences in the vicinity of the genes arrangement on genomes of living organisms. Such nucleotide sequences are called enhancers or promoters. Enhancers and/or promoters become an index to know the state of living organisms in response to stimuli from their environment. Thus, enhancers and/or promoters can effectively be used in a wide range of fields such as the diagnosis of disease, development of therapeutic agents, and detection of hazardous substances. Therefore, the development of technology to screen useful environment specific enhancers and/or promoters from genomes of living organisms has been demanded.
Such methods of screening include the shotgun screening method and the enhancer trap method. The shotgun screening method is a method that is simple in its operation, but its probability of acquiring a promoter is low. According to this method, a vector having a fragmented genome integrated upstream of a marker gene is introduced into a host cell to screen an enhancer and/or a promoter by marker activity provided to the cell by the vector. The enhancer trap method is a time-consuming method of screening due to complex operations because it is necessary to clone cells. According to this method, marker genes that do not have any enhancer and/or promoter are introduced into a cell to be randomly integrated onto a genome. Because only marker genes integrated into the vicinity of an enhancer and/or a promoter are transcribed, enhancers and/or promoters are screened with a high probability from cells cloned using marker activity as an index.
The shotgun screening method and the enhancer trap method can effectively be used for organism species whose genome size is relatively small. However, in the case of screening intended for organism species whose genome size is relatively large, for example, for human beings (genome size: about 3 billion base pairs) or mice (about 3.3 billion base pairs), these methods have problems in terms of simplicity and effectiveness.